Hydrated crystalline form of 2-acrylamido-2-methylpropane sulfonic acid

ABSTRACT

The present invention relates to a hydrated crystalline form of 2-acrylamido-2-methylpropane sulfonic acid having a 2-theta powder X-ray diffraction diagram comprising peaks at 10.58°, 11.2°, 12.65°, 13.66°, 16.28°, 18.45°, 20°, 20.4°, 22.5°, 25.5°, 25.88°, 26.47°, 28.52°, 30.28°, 30.8°, 34.09°, 38.19°, 40.69°, 41.82°, 43.74°, 46.04° degrees (+/−0.1°). The present invention also relates to a production method for this form of 2-acrylamido-2-methylpropane sulfonic acid and a preparation method for an aqueous solution A of a salt of this form of 2-acrylamido-2-methylpropane sulfonic acid, and the (co)polymer of this form of -acrylamido-2-methylpropane sulfonic acid.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 16/926,159, filed on Jul. 10, 2020 (published as U.S.2020-0377449 A1), which is a continuation application of U.S. patentapplication Ser. No. 16/496,031, filed Sep. 20, 2019 (published as U.S.2020-0031765 A1), now U.S. Pat. No. 10,759,746, which is a nationalstage filing under section 371 of International Application No.PCT/FR2018/050652, filed on Mar. 19, 2018, and published on Sep. 27,2018 as WO 2018/172676, which claims priority to French Application No.1752288, filed on Mar. 20, 2017. The entire contents of U.S.2020-0377449 A1, U.S. 2020-0031765 A1, and WO 2018/172676 are herebyincorporated herein by reference.

FIELD OF THE INVENTION

The field of the invention relates to a crystalline form of2-acrylamido-2-methylpropane sulfonic acid (ATBS). More specifically,the present invention relates to a hydrated crystalline form of2-acrylamido-2-methylpropane sulfonic acid. The invention also relatesto the method of producing the hydrated crystalline form of2-acrylamido-2-methylpropane sulfonic acid.

DESCRIPTION OF THE PRIOR ART

2-Acrylamido-2-methylpropane sulfonic acid, also known as ATBS, iswidely used as an additive in acrylic fibers, and as a raw material forproducing polymers used as dispersant, flocculant thickener orsuperabsorbant in diverse sectors such as the oil industry,construction, textiles, water treatment (desalination of sea water,mineral industry, etc.) and cosmetics.

The reaction used in the 2-acrylamido-2-methylpropane sulfonic acidpreparation method is as in the reaction scheme below, in whichacrylonitrile is present in excess so as to be both the reaction solventand a reagent. Acrylonitrile is put in contact with fuming sulfuric acid(oleum) and isobutylene.

A by-product that can be generated during this synthesis is acrylamide.

2-Acrylamido-2-methylpropane sulfonic acid is not soluble in the solventacrylonitrile. Consequently the product of the reaction is in a form ofa crystal suspension in the reaction solvent.

As examples, documents U.S. Pat. No. 6,448,347 and CN 102351744 describea method of producing 2-acrylamido-2-methylpropane sulfonic acidcontinuously. 2-Acrylamido-2-methylpropane sulfonic acid is thenseparated from the acrylonitrile, generally by filtration, then dried.

Drying the 2-acrylamido-2-methylpropane sulfonic acid is necessary toreduce the remaining quantity of acrylonitrile and acrylamide present inthe crystal. These two compounds are classed as carcinogenic, mutagenicor reprotoxic (CMR). It is therefore necessary to proceed with effectivefiltration to remove as much of the acrylonitrile as possible, and thento dry 2-acrylamido-2-methylpropane sulfonic acid to obtain lowacrylonitrile and acrylamide contents.

It is known to the person skilled in the art that2-acrylamido-2-methylpropane sulfonic acid crystals have acrystallographic arrangement that produces a needle-shaped solid.

Needle-shaped crystals are known to the person skilled in the art topresent macroscopic properties that pose difficulties in solid handlingand transport operations (poor solid flowability, clumping, lowresistance to a shear force), processing operations (poor filterability,difficulty in drying, attrition).

For 2-acrylamido-2-methylpropane sulfonic acid, the extra problems thatare met are generally low crystal particle size for needle-shapedcrystals, the density of the solid, and the explosive nature of the finedust.

These macroscopic properties are directly related to the morphology ofthe crystals and to their specific surface area. For a needle-shapedcrystal, the specific surface area is high.

Patents WO 2009/072480, JP 2008/307822 and JP 2003/137857 describe thatthe 2-acrylamido-2-methylpropane sulfonic acid crystals obtained areneedle-shaped.

SUMMARY OF THE INVENTION

The present invention relates to a specific form of2-acrylamido-2-methylpropane sulfonic acid denoted below as “hydratedcrystalline form of 2-acrylamido-2-methylpropane sulfonic acid.”

Another feature of the invention is the method of producing the hydratedcrystalline form of 2-acrylamido-2-methylpropane sulfonic acid.

The invention also relates to an aqueous solution of a2-acrylamido-2-methylpropane sulfonic acid salt prepared from thehydrated crystalline form of 2-acrylamido-2-methylpropane sulfonic acid.

The invention also relates to the use of the hydrated crystalline formof 2-acrylamido-2-methylpropane sulfonic acid for producingwater-soluble, water-swelling or superabsorbent (co)polymers.

Another feature of the invention relates to the use of (co)polymers madefrom the hydrated crystalline form of 2-acrylamido-2-methylpropanesulfonic acid, and more precisely in the field of enhanced oil and gasrecovery.

DESCRIPTION OF THE INVENTION

The present invention relates to a hydrated crystalline form of2-acrylamido-2-methylpropane sulfonic acid having a 2-theta powder X-raydiffraction diagram comprising peaks at 10.58°, 11.2°, 12.65°, 13.66°,16.28°, 18.45°, 20°, 20.4°, 22.5°, 25.5°, 25.88°, 26.47°, 28.52°,30.28°, 30.8°, 34.09°, 38.19°, 40.69°, 41.82°, 43.74°, 46.04° degrees.The uncertainty in these peaks is generally of the order of 0.1°.

X-ray crystallography, radiocrystallography or X-ray diffractometry isan analytical technique for studying the structure of the crystallinematerial on the atomic scale. It uses the physical phenomenon of X-raydiffraction. A diffractometer having a copper source may be used.

A powder formed from a given crystalline phase will always producediffraction peaks in the same directions. So this diffraction diagramforms a real signature of the crystalline phase. It is thereforepossible to determine the nature of each crystalline phase within amixture or a pure product.

This signature is specific to each organic or inorganic compound, andpresents in the form of a list of peaks with positions at the 2θ angle(2-theta).

This technique is used to characterize the material, particularly thedifferent crystalline forms that may exist for a given chemicalmolecule.

The invention also relates to a hydrated crystalline form of2-acrylamido-2-methylpropane sulfonic acid having a Fourier transforminfrared spectrum comprising peaks at 3280 cm⁻¹, 3126 cm⁻¹, 1657 cm⁻¹,1595 cm¹, 1453 cm⁻¹, 1395 cm⁻¹, 1307 cm⁻¹, 1205 cm⁻¹, 1164 cm⁻¹, 1113cm⁻¹, 1041 cm⁻¹, 968 cm⁻¹, 885 cm⁻¹, 815 cm⁻¹, 794 cm⁻¹. The uncertaintyin these peaks is generally of the order of 8 cm⁻¹. Advantageously, thisis the solid spectrum obtained conventionally in a salt such as KBr.

Fourier transform infrared spectroscopy is the analysis of vibrationsemitted, absorbed or diffused by the molecules. This technique issensitive to close interactions (influence of the lattice unit on thebonds). In the majority of cases, the Fourier transform infrared spectrafor different crystalline systems differ significantly. So the Fouriertransform infrared spectrum reflects details about the crystallinestructure of an organic compound.

Generally, and unless otherwise indicated, the X-ray diffraction diagramand the infrared spectrum are obtained at 20° C. and atmosphericpressure of 1 atmosphere (101,325 Pa).

The invention also relates to a hydrated crystalline form of2-acrylamido-2-methylpropane sulfonic acid having minimum ignitionenergy greater than 400 mJ, preferably greater than 500 mJ.

The minimum ignition energy represents the minimum energy that must beprovided to a compound to cause ignition. The energy may be electric orthermal. The minimum ignition energy is an essential piece of data fortaking into account the risk of explosion during product handling(transfer, storage, reaction, shaping, etc.).

The minimum ignition energy depends on the powder's properties(composition) and its macromolecular structure (particle size,crystalline form, specific surface area).

For solids, this energy is the minimum energy of an electrical sparkthat can ignite a cloud of dust. The higher the minimum ignition energy,the lower the risk the solid presents during use, handling, storage.

Minimum ignition energy was measured according to standard NF EN 13821.

The present invention also relates to a hydrated crystalline form of2-acrylamido-2-methylpropane sulfonic acid presenting 4 thermalphenomena with the differential scanning calorimetry technique, at 70°C., 100° C., 150° C. and 190° C. The relative uncertainty when observingthese phenomena is generally of the order of 10° C., advantageously 5°C. or less.

The thermal phenomena are measured by differential scanning calorimetry(DSC). This technique measures the heat variation associated withthermal denaturation of the compound when it is heated at a constantrate, for example with a heating ramp of 10° C./minute.

It is generally recognized that the thermal phenomenon that occurs at190° C. (+/−10° C.) is related to the melting point of2-acrylamido-2-methylpropane sulfonic acid.

In an advantageous manner, the hydrated crystalline form of2-acrylamido-2-methylpropane sulfonic acid according to the inventionhas a water/2-acrylamido-2-methylpropane sulfonic acid molar ratio of 1.

The invention also relates to the method of producing the hydratedcrystalline form of 2-acrylamido-2-methylpropane sulfonic acidcomprising at least the following successive steps:

-   -   1) Mix 2-acrylamido-2-methylpropane sulfonic acid with an        aqueous solution, advantageously for at least 1 minute, to form        suspension A,    -   2) Heat suspension A, advantageously to a temperature of between        40 and 150° C., to produce a solution B of        2-acrylamido-2-methylpropane sulfonic acid,    -   3) Cool solution B, advantageously to a temperature of between        −40 and 100° C., advantageously for a period of between 1 and        1200 minutes, to produce a suspension C of crystals,    -   4) Solid/liquid separation from suspension C and isolate        crystals from suspension C obtained from step 3) in the form of        a composition 1 in which the crystals advantageously represent        between 40 and 99% by weight of composition 1. The crystals        obtained are in the hydrated crystalline form.

The temperature of steps 2) and 3) may vary depending in particular onthe 2-acrylamido-2-methylpropane sulfonic acid concentration. The personskilled in the art will know how to adapt the temperature variation tooptimize crystal formation.

Step 1):

2-Acrylamido-2-methylpropane sulfonic acid comes from a productionmethod as described previously (acrylonitrile, fuming sulfuric acid andisobutylene). 2-Acrylamido-2-methylpropane sulfonic acid may be in theform of fine powder or shaped in a controlled manner by a method such ascompaction, granulation, or extrusion.

The ratio by weight of aqueous solution mixed with2-acrylamido-2-methylpropane sulfonic acid is advantageously between0.1:1 and 5:1, more preferably between 0.2:1 and 3:1.

According to a specific embodiment, the aqueous solution may comprise upto 20% by weight of organic solvent 1, preferably from 1 to 15% byweight of organic solvent 1, more preferably from 2 to 10% by weight oforganic solvent 1.

According to another specific embodiment of the invention, the aqueoussolution comprises at least 80% by weight of water and up to 20% byweight of organic solvent 1, preferably between 85% and 99% by weight ofwater and from 1% to 15% by weight of organic solvent 1, more preferablybetween 90% and 98% by weight of water and from 2% to 10% by weight oforganic solvent 1.

Organic solvent 1 is advantageously chosen from the following compounds:

-   -   organic acids, advantageously carboxylic acids comprising from 1        to 8 carbons,    -   amides comprising advantageously from 1 to 8 carbon atoms,    -   alcohols comprising advantageously from 1 to 8 carbon atoms,    -   ketones comprising advantageously from 1 to 8 carbon atoms,    -   ethers comprising advantageously from 1 to 8 carbon atoms,    -   esters comprising advantageously from 1 to 8 carbon atoms,    -   alkanes comprising advantageously from 1 to 8 carbon atoms,    -   halogenated hydrocarbon compounds comprising advantageously from        1 to 8 carbon atoms,    -   nitriles comprising advantageously from 1 to 8 carbon atoms, or    -   their mixtures.

These compounds may be linear or branched. They may be may be saturatedor comprise unsaturations, for example C═N in the case of nitriles.

Preferably, solvent 1 is chosen from acrylonitrile, isopropanol, aceticacid or their mixtures. Preferably, solvent 1 is acrylonitrile.

Solvent 1 is generally in liquid form at the temperature at which steps2) and 3) are conducted. In addition, it is advantageously miscible withwater.

Solvent 1 may, if need be, solubilize any impurities or by-productspresent with 2-acrylamido-2-methylpropane sulfonic acid used to formsuspension A. By contrast, 2-acrylamido-2-methylpropane sulfonic acid isnot necessarily soluble in solvent 1.

According to another specific embodiment of the invention, the aqueoussolution may comprise at least 80% by weight of water and up to 20% byweight of inorganic acid, preferably between 80% and 99% by weight ofwater and from 1% to 20% by weight of inorganic acid, more preferablybetween 85% and 98% by weight of water and 2% to 15% by weight ofinorganic acid.

Preferably, the inorganic acid is sulfuric acid. In this case, theaqueous solution of sulfuric acid may be prepared by diluting an acidcontaining less than 80% of water, or of a source of SO₃ such as oleumor sulfur trioxide.

So the aqueous solution may comprise at least one organic solvent 1and/or at least one inorganic acid other than2-acrylamido-2-methylpropane sulfonic acid.

The mixing time between the aqueous solution and2-acrylamido-2-methylpropane sulfonic acid is advantageously at least 1minute. During mixing, the aqueous solution may be added sequentiallybefore or after 2-acrylamido-2-methylpropane sulfonic acid. Duringmixing, the aqueous solution and the 2-acrylamido-2-methylpropanesulfonic acid may be added simultaneously.

The mixing temperature is generally below 40° C. The lower temperaturelimit is limited by the melting temperature of the aqueous solution orof suspension A.

The products of step 1) may be mixed using diverse technologies. Asexamples and in a non-limiting manner, we can cite reactors withstirrers, loop reactors, static mixers, microreactors, plug-flowreactors, stirred filter-dryer reactors, for example Nutsche, paddleblenders, double-cone blenders, plow blenders, and disk blenders.

Step 2):

Suspension A obtained in step 1) is heated to a temperature of between40 and 150° C., more preferably between 50 and 120° C. to produce asolution B.

The time for solution B to reach the temperature does not influence thebenefits of the invention.

Diverse technologies may be used to achieve the temperature rise ofsuspension A to produce a solution B. As examples and in a non-limitingmanner, we can cite reactors with stirrers, loop reactors, staticmixers, microreactors, plug-flow reactors, stirred filter-dryerreactors, for example Nutsche, heat exchangers, paddle blenders,double-cone blenders, plow blenders, disk blenders, falling-filmevaporators, wiped-film evaporators, and reboilers.

Step 2) solubilizes 2-acrylamido-2-methylpropane sulfonic acid.

In a specific embodiment of the invention, solution B may undergo asolid/liquid separation operation to remove all insoluble particles.

Step 3:

Solution B obtained in step 2) is cooled to a temperature of between −40and 100° C., more preferably between −20 and 50° C. As alreadyindicated, the person skilled in the art will know how to adjust thetemperature depending on the 2-acrylamido-2-methylpropane sulfonic acidconcentration and/or depending on the melting point of solvent 1 and/orthe inorganic acid of step 1).

In a general manner, the temperature of step 3) is less than thetemperature of step 2).

The cooling time is advantageously between 1 minute and 1200 minutes.

The cooling rate does not have to be constant throughout the process. Asan example, solution B may be cooled by 5° C. per hour during the firstthree hours, and then be cooled at a rate of 10° C. per hour until thefinal temperature is reached.

During the cooling of solution B, crystals of2-acrylamido-2-methylpropane sulfonic acid are formed and precipitate,to form a suspension C.

Diverse technologies may be used to achieve the cooling of solution B toproduce suspension C. As examples and in a non-limiting manner, we cancite reactors with stirrers, loop reactors, static mixers,microreactors, plug-flow reactors, stirred filter-dryer reactors, forexample Nutsche, heat exchangers, paddle blenders, double-cone blenders,plow blenders, disk blenders, falling-film evaporators, wiped-filmevaporators, and non-stirred reactors.

In a specific embodiment of the invention, hydrated crystals of2-acrylamido-2-methylpropanesulfonic acid previously prepared may beadded during this step to modify the formation of suspension C. This iscrystallization seeding, which can lead to better control of thecrystallization temperature, crystal particle size, particle sizedistribution, final product purity and, optionally, yield.

Step 4:

The crystals of hydrated 2-acrylamido-2-methylpropane sulfonic acidcontained in suspension C obtained from step 3) are isolated through aliquid/solid separation step and are presented in the form of acomposition 1. As examples and in a non-limiting manner, we can cite theuse of a centrifugal filter, a decanter, a filter press, a stirredsmoothing filter, a belt filter, a disk filter, or a rotating drumfilter. In a preferred manner, the liquid/solid separation is conductedusing a centrifugal filter. The liquid/solid separation may also beconducted by gravity decantation.

Step 4) is advantageously carried out at a temperature of between −40and 100° C., more preferably between −20 and 50° C.

Preferably after step 4) of liquid/solid separation, the crystals of2-acrylamido-2-methylpropane sulfonic acid are not dried.

Isolated composition 1 has a 2-acrylamido-2-methylpropane sulfonic acidcrystal content advantageously of between 40 and 99%, more preferablybetween 60 and 99% by weight, even more preferably between 60 and 98% byweight. The remainder of composition 1 comprises principally water.

After step 4), the 2-acrylamido-2-methylpropane sulfonic acid crystalsare characterized as being crystals of 2-acrylamido-2-methylpropanesulfonic acid in hydrated form.

Furthermore, the liquid phase obtained after the liquid/solid separationcontains principally water and 2-acrylamido-2-methylpropane sulfonicacid at saturation, and a minor amount of organic solvent 1 and/or theinorganic acid. According to a specific embodiment of the invention,this liquid phase after separation may be used totally or partially inthe aqueous solution in step 1).

Step 5):

In an optional step 5), composition 1 containing the crystals obtainedfrom step 4) is washed using a washing solution.

The washing solution is advantageously an aqueous solution that maycomprise up to 20% of organic solvent 1.

Preferably, the washing solution comprises at least 80% by weight ofwater and up to 20% by weight of organic solvent 1, preferably between80% and 99% by weight of water and from 1% to 20% by weight of organicsolvent 1, more preferably between 85% and 98% by weight of water andfrom 2% to 15% by weight of organic solvent 1.

As already stated, organic solvent 1 is chosen from organic acids,amides, alcohols, ketones, ethers, esters, alkanes, halogenatedhydrocarbon compounds, nitriles, or their mixtures. Preferably, solvent1 is chosen from acrylonitrile, isopropanol, acetic acid or theirmixtures. More preferably, solvent 1 is acrylonitrile.

According to a specific embodiment of the invention, the washing ofcomposition 1 obtained from step 4) is conducted by spraying the washingsolution on said composition 1.

According to another specific embodiment of the invention, the washingof composition 1 obtained from step 4) is conducted by putting saidcomposition 1 into suspension in the washing solution.

The ratio by weight between the aqueous washing solution and thecomposition 1 obtained from step 4) is advantageously between 0.05:1 and10:1 and more preferably between 0.1:1 and 5:1.

This washing step is advantageously conducted at a temperature ofbetween −20 and 100° C. The person skilled in the art will know how toadjust the temperature so as not to solubilize the crystals in hydratedform 2-acrylamido-2-methylpropane sulfonic acid.

According to a specific embodiment, the aqueous washing solution maycomprise up to 60% by weight of 2-acrylamido-2-methylpropane sulfonicacid.

The crystals in hydrated form of 2-acrylamido-2-methylpropane sulfonicacid obtained from optional step 5) may be isolated from the washingsolution by a liquid/solid separation step, in the form of a composition2. As examples and in a non-limiting manner, we can cite the use of avertical or horizontal centrifugal filter, a decanter, a filter press, abelt filter, a disk filter, a pressure filter, or a rotating drumfilter. The liquid/solid separation may also be conducted by gravitydecantation.

According to a specific embodiment of the invention, the washingsolution recovered may be used totally or partially again in step 5),with or without a previous treatment step.

According to a specific embodiment of the invention, the washingsolution may be used totally or partially in the aqueous solution instep 1), with or without a previous treatment step.

Step 6):

In an optional step 6), the composition 2 obtained from step 5) isdried. As examples and in a non-limiting manner, we can cite the use ofall convection, conduction or radiation drying technologies (fluidizedbed dryer, traversed bed dryer, conveyor belt drying, microwave dryingon heated stirred smoothing filter, drying by high frequency radiation,infrared, spray drying).

The drying operation may be conducted at atmospheric pressure or undervacuum.

The drying step may be conducted in a batch or continuous manner

During the production method, i.e. during steps 1) to 6), and regardlessof the step, it is possible to add at least one polymerization inhibitorso as to prevent any polymerization of 2-acrylamido-2-methylpropanesulfonic acid. This inhibitor may be chosen in a non-limiting mannerfrom hydroquinone, paramethoxyphenol, phenothiazine,2,2,6,6-tetramethyl(piperidin-1-yl)oxyl,4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl, phenylene diaminederivatives, or their mixtures.

Preferably, the inhibitor is paramethoxyphenol or4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl.

The quantity of inhibitor added relative to the quantity of2-acrylamido-2-methylpropane sulfonic acid added in step 1) isadvantageously between 0.001% and 5% by weight, more preferably between0.01% and 1% by weight.

The inhibitor may be added during one or more steps of the method.Preferentially, it is added in an additional quantity during step 1).More preferably, the inhibitor forms part of the aqueous solution addedin step 1).

The production method (steps 1) to 6)) may be conducted continuously ordiscontinuously (in batches).

The invention also relates to a preparation method of an aqueoussolution A of a 2-acrylamido-2-methylpropane sulfonic acid salt preparedfrom the hydrated crystalline form.

The preparation method of an aqueous solution A of a2-acrylamido-2-methylpropane sulfonic acid salt comprises the followingsteps:

a) Preparing an aqueous solution X of 2-acrylamido-2-methylpropanesulfonic acid having a concentration advantageously between 1 and 700g/L,

b) Putting in contact and mixing the aqueous solution X with a compoundY chosen from an alkali or alkaline earth metal hydroxide, an alkali oralkaline earth metal oxide, ammonia, an amine having the followingformula NR₁R₂R₃ (R₁, R₂ and R₃ being advantageously hydrocarbon groups,in particular alkyl groups) or an alkali or alkaline earth metalcarbonate.

Step a):

The hydrated crystalline form of 2-acrylamido-2-methylpropane sulfonicacid may be in the form of a fine powder or shaped in a controlledmanner by a method such as compaction, or granulation, or extrusion.

The aqueous solution X of 2-acrylamido-2-methylpropanesulfonic acid isadvantageously prepared by mixing the hydrated crystalline form of2-acrylamido-2-methylpropane sulfonic acid and an aqueous solution Z.

The mixing time between the aqueous solution Z and2-acrylamido-2-methylpropane sulfonic acid is advantageously at least 1minute. During mixing, the aqueous solution Z and the2-acrylamido-2-methylpropane sulfonic acid may be added simultaneously,without a preferred order, or simultaneously.

The mixing temperature is generally below 60° C. The lower temperaturelimit is limited by the crystallization temperature of aqueous solutionZ or of aqueous solution X of 2-acrylamido-2-methylpropane sulfonicacid.

The aqueous solution Z is composed mainly of water, and may contain2-acrylamido-2-methylpropane sulfonic acid or its salt preparedpreviously from any of the bases previously listed (compound Y).

The products of step a) may be mixed using diverse technologies. Asexamples and in a non-limiting manner, we can cite reactors withstirrers, loop reactors, static mixers, microreactors, plug-flowreactors, stirred filter-dryer reactors, for example Nutsche, paddleblenders, double-cone blenders, plow blenders, and disk blenders.

Step b):

Compound Y may be in solid form or liquid form.

According to a specific embodiment of the invention, compound Y is insolid form, preferably in the form of powder or shaped by a method suchas compaction, or granulation, or extrusion.

According to another specific embodiment compound Y is in liquid form,preferably in the form of an aqueous solution Y.

When compound Y is an alkali metal or alkaline earth metal hydroxide, itmay be chosen from sodium hydroxide, potassium hydroxide, lithiumhydroxide, magnesium hydroxide and calcium hydroxide.

When compound Y is an alkaline earth metal oxide, it may be chosen fromcalcium oxide and magnesium oxide.

When compound Y is an amine having formula NR₁R₂R₃ where R₁, R₂ and R₃are independently a hydrogen atom or a carbon chain containing from 1 to22 carbon atoms, advantageously a linear chain, R₁, R₂ and R₃ not beingsimultaneously a hydrogen atom. In a general manner, ammonia (NH₃) ispreferred to amines having formula NR₁R₂R₃.

In a preferred manner, compound Y is an aqueous solution of an alkali oralkaline earth metal hydroxide. Preferably, the alkali metal hydroxideis sodium hydroxide.

When compound Y is in the form of aqueous solution Y, the compound Yconcentration in the solution is advantageously between 0, 1 and 70 mass%.

During the mixing of aqueous solution X with aqueous solution Y, thetemperature is advantageously maintained between −10 and 60° C.,preferably between 0 and 30° C.

The molar ratio of 2-acrylamido-2-methylpropane sulfonic acid andcompound Y is advantageously between 1:0.1 and 1:1.1, more preferablybetween 1:0.5 and 1:1.05.

During mixing, aqueous solution X may be added sequentially before orafter compound Y (or aqueous solution Y). During mixing, aqueoussolution X and compound Y (or its aqueous solution) may be addedsimultaneously.

Preferably, aqueous solution X is added first, followed by compound Y(or its aqueous solution Y).

It is possible, regardless of the step, to add at least onepolymerization inhibitor during the preparation method of solution A ofthe 2-acrylamido-2-methylpropane sulfonic acid salt prepared from thehydrated crystalline solid form. This inhibitor may be chosen in anon-limiting manner from hydroquinone, paramethoxyphenol, phenothiazine,2,2,6,6-tetramethyl(piperidin-1-yl)oxyl,4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl, phenylene diaminederivatives, or their mixtures.

Preferably, the inhibitor is paramethoxyphenol.

The invention also relates to the use of the new hydrated crystallineform of 2-acrylamido-2-methylpropane sulfonic acid for producing(co)polymers. This feature of the invention also covers the use of saltsof the hydrated crystalline form of 2-acrylamido-2-methylpropanesulfonic acid for producing (co)polymers.

Quite unexpectedly, the Applicant has discovered that the (co)polymeraccording to the invention has improved properties especially in termsof filterability and improved chemical and thermal stability compared topolymers prepared from conventional ATBS. These properties areparticularly useful in enhanced oil or gas recovery techniques fromconventional reservoirs, shale or oil sands.

The present invention therefore also relates to a (co)polymer obtainedfrom at least 2-acrylamido-2-methylpropanesulfonic acid, in its acidicand/or salified form, at least a portion of the 2-acrylamido-2 acidmethyl propane sulfonic acid being in hydrated crystalline form andhaving an X-ray powder diffraction pattern comprising peaks at 10.58°,11.2°, 12.65°, 13.66°, 16.28°, 18.45°, 20°, 20.4°, 22.5°, 25.5°, 25.88°,26.47°, 28.52°, 30.28°, 30.8°, 34.09°, 38.19°, 40.69°, 41.82°, 43.74°,46.04° degrees 2-theta (+/−)0.1°.

It can be a copolymer (obtained from several different monomers) or ahomopolymer.

The monomer 2-acrylamido-2-methylpropanesulfonic acid in its hydratedcrystalline form can be in the acid and/or salified form, the salt beingadvantageously obtained from a compound chosen from an alkali metal oralkaline earth metal hydroxide, an alkali or alkaline earth metal oxide,ammonia, an amine of the following formula NR₁R₂R₃ or an alkali metal oralkaline earth metal carbonate.

In general, the salified form of anionic monomers can be obtained beforeand/or during and/or after their polymerization. It is advantageouslyobtained before the polymerization, especially in the case of thehydrated crystalline form of 2-acrylamido-2-methylpropanesulfonic acid.

According to a specific embodiment of the invention, the polymer is ahomopolymer of the hydrated crystalline form of2-acrylamido-2-methylpropane sulfonic acid.

According to another specific embodiment of the invention, the(co)polymer is obtained from at least 2-acrylamido-2-methylpropanesulfonic acid, 50% to 100% of which are the hydrated crystalline form,more preferably 70 to 100%, even more preferably 100%.

The (co)polymer according to the invention is advantageously obtainedfrom 1 to 100 mol % of 2-acrylamido-2-methylpropanesulfonic acid,preferably between 2 and 60 mol % of2-acrylamido-2-methylpropanesulfonic acid, even more preferably between3 and 25 mol % of 2-acrylamido-2-methylpropanesulfonic acid; 50% to 100%of 2-acrylamido-2-methylpropanesulfonic acid are advantageously in thehydrated crystalline form, more preferably 70 to 100%, and even morepreferably 100%.

In general, the skilled person will know, if necessary, how to adjustthe amount of optional additional monomers (anionic and/or cationicand/or zwitterionic) listed below to reach 100 mol %.

According to another particular embodiment of the invention, the(co)polymer may be obtained from 2-acrylamido-2-methylpropanesulfonicacid of which 50% to 100% are advantageously in the hydrated crystallineform (more advantageously 70 to 100%, and even more preferably 100%) andfrom at least one non-ionic monomer and/or at least one anionic monomerand/or at least one cationic monomer and/or a zwitterionic monomer.

According to another particular embodiment of the invention, the polymeris a copolymer of the hydrated crystalline form of2-acrylamido-2-methylpropanesulfonic acid and at least one non-ionicmonomer.

The non-ionic monomer may notably be selected from the group comprisingwater-soluble vinyl monomers, and particularly acrylamide;N-isopropylacrylamide; N,N-dimethylacrylamide; N-vinylformamide;acryloyl morpholine; N,N-diethyl acrylamide; N-tert-butyl acrylamide;N-tert-octylacrylamide; N-vinylpyrrolidone; N-vinylcaprolactam;N-vinyl-imidazole, hydroxyethyl methacrylamide, hydroxypropylacrylate,isoprenol and diacetone acrylamide. Advantageously, the non-ionicmonomer is acrylamide.

According to a particular embodiment, the copolymer is advantageouslyobtained from 1 to 99 mol % of non-ionic monomer(s), preferably between40 and 95 mol % and more preferably between 45 and 90 mol %, relative tothe total number of monomers. In this case, the copolymer isadvantageously obtained from 0.1 to 99 mol % of2-acrylamido-2-methylpropane sulfonic acid, 50% to 100% being inhydrated crystalline form, more preferably from 70 to 100%, even morepreferably 100%.

The anionic monomer(s) may have acrylic, vinyl, maleic, fumaric,malonic, itaconic, allylic functional groups and contain a carboxylate,phosphonate, phosphate, sulfate, sulfonate group or another anionicgroup. The anionic monomer may be in acid form and/or in the form of analkaline earth metal salt, an alkali metal salt or an ammonium salt.Examples of suitable monomers comprise acrylic acid, methacrylic acid,itaconic acid, crotonic acid, maleic acid, fumaric acid, acrylamideundecanoic acid, acrylamide 3-methylbutanoic acid, maleic anhydride;monomers of the strong acid type having for example a function of thesulfonic acid or phosphoric acid type, such as vinylsulfonic acid,vinylphosphonic acid, allylsulfonic acid, methallylsulfonic acid,2-methylidenepropane-1,3 -disulfonic acid, 2-sulfoethylmethacrylate,sulfopropylmethacrylate, sulfopropylacrylate, allylphosphonic acid,styrene sulfonic acid, 2-acrylamido-2-methypropane disulfonic acid; andsalts of these monomers like their alkali metal, alkaline earth metal,or ammonium salts. In this list, the strong acid monomers mentionedhaving a sulfonic acid function do not include the hydrated crystallineform of 2-acrylamido-2-methylpropane sulfonic acid according to theinvention.

According to a particular embodiment, the copolymer is advantageouslyobtained from 1 to 99 mol % of anionic monomer(s), preferably between 2and 60 mol % and more preferably between 3 and 25 mol %, relative to thetotal number of monomers. These percentages include the monomer of thehydrated crystalline form of 2-acrylamido-2-methylpropane sulfonic acidaccording to the invention.

The cationic monomer(s) that may be used in the invention mayparticularly be selected from monomers of the acrylamide, acrylic,vinyl, allyl or maleic type having a phosphonium or quaternary ammoniumfunction. Mention may be made, in particular and in a non-limiting way,of quaternized dimethylaminoethyl acrylate (ADAME), quaternizeddimethylaminoethyl methacrylate (MADAME), dimethyldiallylammoniumchloride (DADMAC), acrylamido propyltrimethyl ammonium chloride (APTAC)and methacrylamido propyltrimethyl ammonium chloride (MAPTAC). Thequaternizing agent may be chosen from alkyl chlorides, dialkyl sulphatesor alkyl halides. Preferably, the quaternizing agent is chosen frommethyl chloride or diethyl sulphate.

The zwitterionic monomer may be of the type acrylamide, acrylic, vinyl,allyl or maleic having an amine or quaternary ammonium function and anacid function like a carboxylic, sulfonic or phosphoric acid. Mentionmay be made, specifically and in a non-limiting manner, ofdimethylaminoethyl acrylate derivatives, such as2-((2-(acryloyloxy)ethyl) dimethylammonio) ethane-1-sulfonate,3-((2-(acryloyloxy)ethyl) dimethylammonio) propane-1-sulfonate,4-((2-(acryloyloxy)ethyl) dimethylammonio) butane-1-sulfonate,[2-(acryloyloxy)ethyl)] (dimethylammonio) acetate, dimethylaminoethylmethacrylate derivatives such as 2-((2-(methacryloyloxy) ethyl)dimethylammonio) ethane-1-sulfonate, 3-((2-(methacryloyloxy) ethyl)dimethylammonio) propane-1-sulfonate, 4-((2-(methacryloyloxy) ethyl)dimethylammonio) butane-1-sulfonate, [2-(methacryloyloxy) ethyl](dimethylammonio) acetate, dimethylamino propylacrylamide derivativessuch as 2-((3-acrylamidopropyl) dimethylammonio) ethane-1-sulfonate,3-((3-acrylamidopropyl) dimethylammonio) propane-1-sulfonate,4-((3-acrylamidopropyl) dimethylammonio) butane-1-sulfonate,[3-(acryloyloxy) propyl] (dimethylammonio) acetate, dimethylamino propylmethylacrylamide derivatives such as 2-((3-methacrylamidopropyl)dimethylammonio) ethane-1-sulfonate, 3-((3-methacrylamidopropyl)dimethylammonio) propane-1-sulfonate, 4-((3-methacrylamidopropyl)dimethylammonio) butane-1-sulfonate and [3-(methacryloyloxy)propyl)](dimethylammonio) acetate.

Monomers with a hydrophobic nature may also be used in the invention.They are preferably selected from the group consisting of (meth)acrylicacid esters having an alkyl, arylalkyl, propoxylated, ethoxylated, orethoxylated and propoxylated chain; (meth)acrylamide derivatives havingan alkyl, arylalkyl, propoxylated, ethoxylated, ethoxylated andpropoxylated, or dialkyl chain; alkyl aryl sulfonates.

When a monomer having a hydrophobic nature is used, the quantity thereoflies advantageously within the range between 0.001 and 3 mol % inrelation to the total quantity of monomers.

Monomers with a fluorescent function may also be used in the scope ofthe invention. A monomer with a fluorescent function may be detected byany appropriate method, for example by fluorimetry with a fixedwavelength fluorimeter. Generally, the monomer having a fluorescentfunction is detected at the excitation and emission maxima, which can bedetermined using a scanning fluorimeter.

Those monomers having a fluorescent function are chosen from, forexample, monomers comprising sodium sulfonate styrene and sulfonicstyrene.

According to the invention, the (co)polymer used may have a linear,branched, cross-linked, star-shaped or comb-shaped structure. Thesestructures may be obtained by the selection of the initiator, transferagent, polymerization technique, such as controlled radicalpolymerization known as RAFT (reversible-addition fragmentation chaintransfer), NMP (nitroxide-mediated polymerization) or ATRP(atom-transfer radical polymerization), incorporation of structuralmonomers, or concentration, etc.

Generally, the (co)polymer does not require the development of anyparticular polymerization method. Indeed, it may be obtained accordingto polymerization techniques known by a person skilled in the art. Itmay notably be solution polymerization, gel polymerization,precipitation polymerization, emulsion polymerization (aqueous orinverse), suspension polymerization, reactive extrusion polymerization,or micellar polymerization.

According to a specific embodiment of the invention, the (co)polymer maybe post-hydrolyzed. Post-hydrolysis is the reaction of the (co)polymerafter polymerization. This step consists in reacting the hydrolyzablefunctional groups on the nonionic monomers, such as amide or esterfunctions, with a base. During this (co)polymer post-hydrolysis step,the number of carboxylic acid functions increases. The reaction betweenthe base and the amide or ester functions produces carboxylate groups inthe (co)polymer product.

The (co)polymer may be in the form of a liquid, gel or solid when itspreparation includes a drying step such as spray drying, tumble drying,drying by electromagnetic radiation (microwave, high frequency), orfluidized bed drying.

According to the invention, the (co)polymer may be linear, structured orcrosslinked. Structured (co)polymer denotes a non-linear (co)polymerthat has side chains so as to obtain, when this (co)polymer is dissolvedin water, a high state of tangling leading to very high viscosities atlow gradients.

The (co)polymer may in addition be structured or crosslinked:

-   -   by at least one structure agent, which can be chosen from the        group comprising unsaturated polyethylenic monomers (having at        least two unsaturated functions), such as for example vinyl,        allyl, acrylic and epoxy functions and for example mention may        be made of methylene-bis-acrylamide (MBA), triallyamine,        tetraallylammonium chloride, 1,2-dihydroxyethylene        bis-(N-acrylamide), and/or    -   by macroinitiators such as polyperoxides, polyazoics and poly        transfer agents such as polymercaptan (co)polymers, and polyols,        and/or    -   by functionalized polysaccharides.

The quantity of branching/crosslinking agent in the monomer mixture isadvantageously less than 4% by weight relative to the monomer content,more advantageously less than 1%, and even more advantageously less than0.5%. According to a specific embodiment, it may at least equal to0.00001% by weight in relation to the monomer content.

According to a specific embodiment, the (co)polymer may comprise atleast one LCST group.

According to the general knowledge of a person skilled in the art, aLCST group corresponds to a group whose water solubility for adetermined concentration is modified beyond a certain temperature and asa function of the salinity This is a group having a heating transitiontemperature defining its lack of affinity with the solvent medium. Thelack of affinity with the solvent results in opacification or loss oftransparency, which may be due to precipitation, aggregation,gelification, or viscosification of the medium. The minimum transitiontemperature is known as “LCST” (Lower Critical Solution Temperature).For each concentration of the LCST group, a heating transitiontemperature is observed. It is greater than the LCST, which is theminimum point in the curve. Below this temperature, the (co)polymer issoluble in water; above this temperature, the (co)polymer loses itssolubility in water.

According to a specific embodiment, the (co)polymer may comprise atleast one UCST group.

According to the general knowledge of a person skilled in the art, aUCST group corresponds to a group whose water solubility for adetermined concentration is modified beyond a certain temperature and asfunction of the salinity This is a group having a cooling transitiontemperature defining its lack of affinity with the solvent medium. Thelack of affinity with the solvent results in opacification or loss oftransparency, which may be due to precipitation, aggregation,gelification, or viscosification of the medium. The maximum transitiontemperature is known as “UCST” (Upper Critical Solution Temperature).For each concentration of the UCST group, a cooling transitiontemperature is observed. It is lower than the UCST, which is the maximumpoint in the curve. Above this temperature, the (co)polymer is solublein water; below this temperature, the (co)polymer loses its watersolubility.

According to the invention, the (co)polymer has an advantageously highmolecular weight. “High molecular weight” denotes molecular weights ofat least 1 million g/mol, preferably between 2 and 40 millions g/mol,more preferably between 5 and 30 million g/mol. Molecular weight isunderstood as average molecular weight by weight.

According to one embodiment of the invention, the copolymer may beobtained by (co)polymerization of at least one water-soluble monomer andat least one monomer of the hydrated crystalline form of2-acrylamido-2-methylpropane sulfonic acid and/or of one of its salts.

Broadly speaking, unless otherwise indicated,“2-acrylamido-2-methylpropane sulfonic acid in hydrated crystallineform” denotes the acid form and/or the salified form. The same appliesto the anionic monomers mentioned in the description of the invention,which may denote the acid and/or salified forms like, for example, foracrylic acid.

The salt form is advantageously obtained from a compound chosen fromamong an alkali or alkaline earth metal hydroxide, an alkali or alkalinemetal earth oxide, ammonia, an amine having the following formulaNR₁R₂R₃ (R₁, R₂ and R₃ being advantageously hydrocarbon groups, inparticular alkyl groups) or an alkali or alkaline earth metal carbonate.A preferred alkaline metal is sodium.

The acid form of a monomer can be salified before and/or during and/orafter the (co)polymerization of the monomer or monomers.

The (co)polymer of the invention is preferably water-soluble.

Advantageously, the (co)polymer has a molecular weight of between 5000and 40,000,000 g/mol, preferably between 1,250,000 and 35,000,000 andeven more preferably between 2,750,000 and 30,000,000 g/mol by weight.

The molecular weight is determined by the intrinsic viscosity of the(co)polymer. The intrinsic viscosity may be measured by methods known tothe person skilled in the art and may be calculated from lower viscosityvalues for different (co)polymer concentrations by a graphic methodconsisting in recording the lower viscosity values (y-axis) over theconcentration (x-axis) and extrapolating the curve to zeroconcentration. The intrinsic viscosity value is recorded on the y-axisor using the least squares method. The molecular weight may then bedetermined by the Mark-Houwink equation:[η]=KM ^(α)

[η] represents the intrinsic viscosity of the (co)polymer determined bythe method for measuring viscosity in solution.

K represents an empirical constant.

M represents the molecular weight of the (co)polymer.

α represents the Mark-Houwink coefficient.

K and α depend on the specific (co)polymer-solvent system.

Another feature of the invention relates to the use of (co)polymers madefrom the hydrated crystalline form of 2-acrylamido-2-methylpropanesulfonic acid or at least one of its salts. In these (co)polymers,2-acrylamido-2-methylpropane sulfonic acid may be partially neutralizedbefore, during, or after the (co)polymerization of2-acrylamido-2-methylpropane sulfonic acid. More precisely, theinvention relates to the use of these (co)polymers in the oil and gas,hydraulic fracturing, paper, water treatment, construction, mining,cosmetics, textile, or detergent industry. Preferably, the (co)polymersare used in the field of enhanced oil and gas recovery.

The invention and the benefits that flow from it will be clearer uponreading the following figures and examples, given to illustrate theinvention and not to limit it in any way.

DESCRIPTION OF FIGURES

FIG. 1 illustrates the proton NMR spectrum of the2-acrylamido-2-methylpropane sulfonic acid crystals obtained accordingto examples 1 and 2.

FIG. 2 illustrates the X-ray diffraction diagram of the crystalsobtained according to example 1.

FIG. 3 illustrates the X-ray diffraction diagram of the crystalsobtained according to example 2.

FIG. 4 illustrates the Fourier transform infrared spectrum of thecrystals obtained in example 1.

FIG. 5 illustrates the X-ray diffraction diagram of the crystalsobtained according to example 2.

FIG. 6 illustrates the thermogram of the crystals obtained according toexample 1.

FIG. 7 illustrates the thermogram of the crystals obtained according toexample 2.

FIG. 8 illustrates the particle size graph of the crystals obtainedaccording to example 1.

FIG. 9 illustrates the particle size graph of the crystals obtainedaccording to example 2.

FIG. 10 corresponds to the optical microscope observation of thecrystals obtained according to example 1.

FIG. 11 corresponds to the optical microscope observation of thecrystals obtained according to example 2.

FIG. 12 corresponds to the scanning electron microscope observation ofthe crystals obtained according to example 1.

FIG. 13 corresponds to the scanning electron microscope observation ofthe crystals obtained according to example 2.

FIG. 14 illustrates the loss of viscosity as a function of ATBS form andiron content for a copolymer.

FIG. 15 illustrates the viscosity loss as a function of ATBS form at 90°C. aging for a copolymer.

FIG. 16 illustrates the loss of viscosity as a function of ATBS form andiron content for a homopolymer.

EXAMPLE EMBODIMENTS OF THE INVENTION Example 1: Synthesis of2-acrylamido-2-methylpropane Sulfonic Acid

To a stirred 2000-mL jacketed reactor, 1522 grams of acrylonitrile wasadded containing 0.4% of water by weight and 180 grams of fumingsulfuric acid titrating at 104% H₂SO₄ (18% Oleum). The mixture wasstirred for 1 hour and cooled via the reactor jacket, which held thetemperature of the sulfonating mixture at −20° C.

To the previous sulfonating mixture, 97 grams of isobutylene was added,at a flow rate of 1.6 grams/minute.

The temperature of the mixture was controlled at 45° C. whileisobutylene was added. The particles of 2-acrylamido-2-methylpropanesulfonic acid precipitate in the mixture and the solid content was about20% by weight. The reaction mixture was filtered on a Buchner filter anddried under vacuum at 50° C. The solid obtained was2-acrylamido-2-methylpropane sulfonic acid; it was present in the formof a very fine white powder.

From observations made with an optical microscope (FIG. 10 ) and ascanning electron microscope (FIG. 12 ), the crystals wereneedle-shaped.

Example 2: Formation of the Hydrated Crystalline form of2-acrylamido-2-methylpropane Sulfonic Acid

To a 2000-mL jacketed reactor, 500 grams of 2-acrylamido-2-methylpropanesulfonic acid obtained in example 1 and 460 grams of sulfuric acid at aconcentration of 10% H₂SO₄ were added.

250 mg of 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl was added to thepreceding mixture.

The mixture was stirred for 10 minutes, at 20° C., to form suspension A.

Suspension A was heated to a temperature of 60° C. and maintained atthis temperature for 20 minutes to form solution B.

Solution B was cooled to a temperature of 10° C. The cooling timebetween 60° C. and 10° C. was 6 hours. Suspension C of crystals of2-acrylamido-2-methylpropane sulfonic acid was obtained. Suspension Cwas filtered on a vertical Robatel centrifugal dryer. A solid ofcomposition 1 was obtained, containing 80% by weight of2-acrylamido-2-methylpropane sulfonic acid crystals.

From observations made with an optical microscope (FIG. 11 ) and ascanning electron microscope (FIG. 13 ), the crystals were cubic-shaped.

Example 3: NMR Analysis of Products from Examples 1 and 2

The 2-acrylamido-2-methylpropane sulfonic solid obtained in example 1and its hydrated crystalline form obtained in example 2 were analyzed byproton nuclear magnetic resonance (NMR).

The samples were dissolved in D₂O. The Bruker NMR machine had afrequency of 400 MHz, and was equipped with a 5 mm BBO BB-¹H probe.

The two proton spectra (FIG. 1 ) were identical and the peak assignmentsconformed to the molecular structure of 2-acrylamido-2-methylpropanesulfonic acid.

Example 4: X-Ray Diffraction Analysis

The solids obtained in examples 1 and 2 were previously ground to formpowders and were analyzed by X-ray diffraction over an angular rangefrom 10 to 90°. The equipment used was a Rigaku miniflex IIdiffractometer equipped with a copper source.

We observed that the solid obtained from example 2 (FIG. 3 ) has a2-theta X-ray diffraction diagram with the following characteristicpeaks:

10.58°, 11.2°, 12.65°, 13.66°, 16.28°, 18.45°, 20°, 20.4°, 22.5°, 25.5°,25.88°, 26.47°, 28.52°, 30.28°, 30.8°, 34.09°, 38.19°, 40.69°, 41.82°,43.74°, 46.04° 2-Theta degrees (+/−0.1°).

Example 5: Fourier Transform Infrared Measurement

The equipment for Fourier transform infrared measurement was the PerkinElmer Spectrum 100, whose precision is 8 cm⁻¹.

The solids obtained in examples 1 and 2 were sieved at 100 μm. Theparticles remaining on the sieve were dried and put in the oven at 60°C. for at least 4 hours.

10 mg of solid was weighed precisely and mixed with 500 mg of potassiumbromide (KBr). The mixture was then compacted in a hydraulic press undera pressure of at least 10 bars.

We observed that the following bands (FIG. 5 ) are characteristic of thehydrated crystalline form of 2-acrylamido-2-methylpropane sulfonic acid:

3280 cm⁻¹, 3126 cm⁻¹, 1657 cm⁻¹, 1595 cm⁻¹, 1453 cm⁻¹, 1395 cm⁻¹, 1307cm⁻¹, 1205 cm⁻¹, 1164 cm⁻¹, 1113 cm⁻¹, 1041 cm⁻¹, 968 cm⁻¹, 885 cm⁻¹,815 cm⁻¹, 794 cm⁻¹.

The infrared spectrum of the solid according to example 1 (FIG. 4 ) didnot present the same peaks.

Example 6: Differential Scanning Calorimetry (DSC)

The device used was a DSC131 EVO by Setaram.

The solids obtained in examples 1 and 2 were analyzed with a 10°C./minute heating ramp under a flow of nitrogen. The initial temperaturewas 30° C.; the product was heated to 220° C.

The thermogram of the crystals in example 1 (FIG. 6 ) showed a thermaleffect at a temperature of 191.5° C., which is generally considered asthe melting/degradation point of 2-acrylamido-2-methylpropane sulfonicacid.

The thermogram of the crystals from example 2 (FIG. 7 ) showed 3additional thermal phenomena visible at 70.8; 103.4 and 152.2° C. Thepeak at 187.4° C. is related to the degradation of the molecule of2-acrylamido-2-methylpropane sulfonic acid.

As a comparison, the thermogram of the crystals from example 1 did notpresent a degradation peak at 191.5° C. (FIG. 6 ).

Example 7: Acid-Base Titration

To a 1000-mL beaker, 500 mL of demineralized water and 100 g of theobtained from example 1 were added. A magnetic bar was added to be ableto mix the solution.

A graduated burette was filled with 30% sodium hydroxide.

A pH meter was added to be able to monitor the pH during the sodiumhydroxide addition.

Initially the pH of the aqueous solution was less than 1 Sodiumhydroxide was added until a pH of 7 was obtained.

64 g of 30% sodium hydroxide was added.

The molar mass of 2-acrylamido-2-methylpropane sulfonic acid was 207g/mol. Calculating the equivalence point showed that the solid obtainedin example 1 contained 99% by weight of 2-acrylamido-2-methylpropanesulfonic acid (titration of the acid function).

The solid obtained in example 2 was titrated using the same protocol. 59g of sodium hydroxide was added to 100 g of the solid obtained fromexample 2. Calculating the equivalence point showed that the solidobtained in example 2 contained 92% by weight of2-acrylamido-2-methylpropane sulfonic acid.

The remaining 8% was water. This 2-acrylamido-2-methylpropane sulfonicacid/H₂O mass ratio (92/8) corresponded to a 1:1 molar ratio.

The solid obtained in example 2 was therefore a hydrated crystallineform of 2-acrylamido-2-methylpropane sulfonic acid.

Example 8: Measurement of the Minimum Ignition Energy (MIE)

Minimum ignition energy was measured according to standard NF EN 13821.

The explosimeter was a vertical Hartmann tube. The dust dispersionsystem was a mushroom system.

The total induction was less than 25 microhenry. The discharge voltagewas comprised between 5 kV and 15 kV. The electrodes were made of brassand spaced at least 6 mm apart.

Different energies and dispersed mass were tested and summarized in thefollowing tables.

It appears clearly that the hydrated crystalline form presents asubstantially lower explosion risk than the needle-shaped form obtainedin example 1.

TABLE 1 Determination of the solid MIE from example 1 Mass of Ignition?Energy dispersed Number of Yes (Y) (mJ) solid (g) dispersions No (N)Flame Pressure 1000 0.5 2 Y Small Small 500 0.5 3 Y Average Average 3000.5 3 Y Average Average 100 0.5 20 N 200 0.5 20 N 200 1 20 N 200 2 20 N200 3 7 Y Average Small 100 3 20 N 100 5 20 N 100 7 20 N 100 10 20 N 1001 20 N 100 2 20 N

TABLE 2 Determination of the solid MIE from example 2 Mass of Ignition?Energy dispersed Number of Yes (Y) (mJ) solid (g) dispersions No (N)Flame Pressure 1000 0.5 20 N 1000 1 20 N 1000 2 20 N 1000 3 20 N 1000 520 N 1000 7 20 N 1000 10 20 N 1000 15 13 Y Small Average 500 15 20 N 50020 20 N 500 10 20 N 500 7 20 N 500 5 20 N 500 3 20 N 500 2 20 N 500 1 20N 500 0.5 20 N

Example 9: Particle Size Measurement

The solids obtained in examples 1 and 2 were analyzed by laserdiffraction to determine their particle size distribution.

The equipment used was a Cilas 1190.

For the crystals in example 1, the d₅₀ value was about 40 μm and 90% ofthe particles were smaller than 200 μm (FIG. 8 ).

For the crystals in example 2, the d₅₀ value was about 600 μm and 90% ofthe particles were smaller than 1500 μm (FIG. 9 ). The crystalscontained less than 10% of particles smaller than 300 μm.

Example 10: Measurement of Specific Surface Area

The solids obtained in examples 1 and 2 were degassed at ambienttemperature for 24 hours.

The device for measuring specific surface area by sorptometry was aTriStar II Micromeritics device coupled with a Micromeritics SmartVacPrep. The measurement temperature was −196° C.

TABLE 3 Specific surface area of 2-acrylamido- 2-methylpropane sulfonicacids Origin of the Specific surface 2-acrylamido-2-methylpropanesulfonic acid area (m²/g) Example 1 (counter-example) 1.32 +/− 0.14Example 2 (invention) 0.06 +/− 0.01

Example 11: Preparation Protocol for the Sodium Salt of the HydratedCrystalline Form of 2-acrylamido-2-methylpropane Sulfonic Acid

To a jacketed 2000-mL reactor equipped with a condenser, a pH meter anda stirrer, 500 grams of the hydrated crystalline form ofacrylamido-2-methylpropane sulfonic acid from example 2 and 770 grams ofwater were added. The mixture had a pH of less than 1.

A solution of 50% concentration by weight sodium hydroxide was preparedin a dropping funnel. The caustic solution was added to the reactionmixture for 120 minutes. The temperature was controlled to be less than30° C.

During the sodium hydroxide addition, the pH remained under 5.

175 grams of 50% concentration by weight sodium hydroxide solution wasadded.

The mixture obtained was a solution of the 2-acrylamido-2-methylpropanesulfonic acid sodium salt at a concentration of 35% by weight.

Example 12 Preparation of Copolymer P1 ofacrylamide/2-acrylamido-2-methylpropane Sulfonic Acid of HydratedCrystalline Form (75/25 Mole %)

549.5 g of deionized water, 520.5 of acrylamide in 50% solution, 97.6 gof 50% sodium hydroxide solution, 16.2 g of urea and 316.2 g of2-acrylamido-2-methylpropanesulfonic acid crystals obtained in Example2g are added to a 2000 ml beaker.

The solution thus obtained is cooled between 0 and 5° C. and transferredto an adiabatic polymerization reactor, nitrogen bubbling is carried outfor 30 minutes to remove any trace of dissolved oxygen.

Then added in the reactor:

0.75 g of 2,2′-azobisisobutyronitrile,

1.5 ml of a solution containing 5 g/l of 2,2′-azobis[2-(2-imidazolin-2-yl) propane dihydrochloride],

1.5 ml of a solution containing 3 g/l of sodium hypophosphite,

2.25 ml of a solution containing 1 g/l of tert-butyl hydroperoxide,

2.25 ml of a 1 g/l solution of ammonium sulfate and iron (II)hexahydrate (Mohr salt).

After a few minutes the nitrogen inlet is closed and the reactor isclosed. The polymerization reaction takes place for 1 to 5 hours until apeak temperature is reached. The rubbery gel obtained is chopped intoparticles with a size of between 1 and 6 mm.

The gel is then dried and milled to obtain the polymer in powder form.

Example 13 Preparation of Copolymer P′1 ofacrylamide/2-acrylamido-2-methylpropanesulfonic Acid that is not theHydrated Crystalline Form (75/25 Mole %)

The copolymer is prepared as in Example 12, replacing the crystallineform 2-acrylamido-2-methylpropane sulfonic acid hydrate (Example 2) withthe non hydrated crystalline form of2-acrylamido-2-methylpropanesulfonic acid obtained in Example 1.

Example 14 Measurement of the Resistance to Chemical Degradation ofSolutions of Copolymers P1 and P′1 of Equivalent Molecular Weight

Resistance to chemical degradation tests of polymers P1 and P′1 with amolecular weight of 9 million were carried out under aerobic conditionsin the presence of different concentrations of iron (II) (2, 5, 10 and20 ppm) in a brine composed of water, 37000 ppm NaCl, 5000 ppm Na₂SO₄and 200 ppm NaHCO₃. These tests were carried out on a polymer preparedfrom the non-crystalline form of 2-acrylamido-2-methylpropanesulfonicacid or of at least one of its salts (P′1) and on a polymer preparedfrom the crystalline form of 2-acrylamido-2-methylpropanesulfonic acidor at least one of its salts (P1). Both polymers have the same chemicalcomposition. The results obtained after 24 hours of bringing the polymersolution into contact with the contaminant are shown in FIG. 14 .

We can observe that, for each concentration of iron (II), the polymer P1loses less viscosity than the polymer P′1 equivalent.

Example 15 Measurement of Resistance to Thermal Degradation of Solutionsof Polymers of Equivalent Molecular Weight

Tests of resistance to thermal degradation of polymers P1 and P′ 1 witha molecular weight of 9 million were carried out anaerobically at anactive concentration of 2000 ppm in a brine composed of water, 30000 ppmof NaCl and 3000 ppm CaCl₂.2H₂O. These tests were carried out on apolymer made from the non-crystalline form of2-acrylamido-2-methylpropanesulfonic acid or at least one of its salts(P′1) and on a polymer made from the crystalline form of2-acrylamido-2-methylpropanesulfonic acid or at least one of its salts(P1). Both polymers have the same chemical composition. The polymersolutions were aged for 6 months at 90° C. The results obtained areshown in FIG. 15 in terms of loss of viscosity. We can observe that thepolymer P1 loses less viscosity than the polymer P′1 equivalent.

Example 16 Preparation of Homopolymers P2 from the Hydrated CrystallineForm of 2-acrylamido-2-methylpropanesulfonic Acid

390.5 g of deionized water, 262 g of 50% sodium hydroxide solution and847.5 g of 2-acrylamido-2-methylpropanesulfonic acid crystals obtainedin Example 2 are added to a 2000 ml beaker.

The solution thus obtained is cooled between 5 and 10° C. andtransferred to an adiabatic polymerization reactor, a nitrogen bubblingis carried out for 30 minutes to remove any trace of dissolved oxygen.

Then added in the reactor:

0.45 g of 2,2′-azobisisobutyronitrile,

1.5 ml of a solution containing 2.5 g/l of 2,2′-azobis[2-(2-imidazolin-2-yl) propane dihydrochloride],

1.5 ml of a 1 g/l solution of sodium hypophosphite,

1.5 ml of a solution containing 1 g/l of tert-butyl hydroperoxide,

1.5 ml of a 1 g/l solution of ammonium sulfate and iron (II) hexahydrate(Mohr salt).

After a few minutes the nitrogen inlet is closed and the reactor isclosed. The polymerization reaction takes place for 2 to 5 hours until apeak temperature is reached. The rubbery gel obtained is chopped anddried to obtain a coarse powder which is itself ground and sieved toobtain the polymer in powder form.

Example 17 Preparation of Homopolymers P′2 from2-acrylamido-2-Methylpropane Sulfonic Acid that is not the HydratedCrystalline Form

The polymers are prepared as in Example 16, replacing the hydratedcrystalline form of 2-acrylamido-2-methylpropanesulfonic acid with2-acrylamido-2-methylpropanesulfonic acid synthesized in example 1 thatis not the hydrated crystalline form.

Example 18 Measurement of Resistance to Chemical Degradation ofSolutions of Polymers P2 and P′2

Resistance tests to chemical degradation of polymers P2 and P′2 with amolecular weight of 5.3 million Da were performed under aerobicconditions in the presence of various iron (II) concentrations (2, 5, 10and 20 ppm) in brine composed of water, 37000 ppm NaCl, 5000 ppm Na₂SO₄and 200 ppm NaHCO₃. These tests were carried out on a polymer preparedfrom the non-crystalline form of 2-acrylamido-2-methylpropanesulfonicacid or of at least one of its salts (P′2) and on a polymer preparedfrom the crystalline form of 2-acrylamido-2-methylpropanesulfonic acidor at least one of its salts (P2). Both polymers have the same chemicalcomposition. The results obtained after 24 hours of bringing the polymersolution into contact with the contaminant are shown in FIG. 16 .

We can observe that for each iron (II) concentration, the polymer P2loses less viscosity than the equivalent polymer P′2.

Example 19 Preparation of post Hydrolyzed Copolymer P3 ofacrylamide/2-acrylamido-2-Methylpropane Sulfonic acid of HydratedCrystalline Form (75/25 Mole %)

In a 2000 ml beaker are added 761.9 g of deionized water, 574.2 g ofacrylamide in 50% solution, 35.9 g of 50% sodium hydroxide solution,11.7 g of urea and 116.3 g 2-acrylamido-2-methylpropanesulfonic acidcrystals obtained in Example 2.

The solution thus obtained is cooled between 0 and 5° C. and transferredto an adiabatic polymerization reactor, nitrogen bubbling is carried outfor 30 minutes to remove any trace of dissolved oxygen.

Then added in the reactor:

0.45 g of 2,2′-azobisisobutyronitrile,

1.5 ml of a solution containing 5 g/l of 2,2′-azobis[2-(2-imidazolin-2-yl) propane dihydrochloride],

1.5 ml of a 1 g/l solution of sodium hypophosphite,

2.25 ml of a solution containing 1 g/l of tert-butyl hydroperoxide,

3.0 ml of a 1 g/l solution of ammonium sulfate and iron (II) hexahydrate(Mohr salt).

After a few minutes the nitrogen inlet is closed and the reactor isclosed. The polymerization reaction takes place for 2 to 5 hours until apeak temperature is reached. The rubbery gel obtained is chopped intoparticles with a size of between 1 and 6 mm.

500.0 g of previously minced gel are then mixed with 18.0 g of 50%sodium hydroxide solution, the mixture is heated and maintained at atemperature of 90° C. for a duration of 90 minutes.

The gel is then dried and milled to obtain the polymer in powder form.

Example 20 Preparation of Post Hydrolyzed P′3 copolymer ofacrylamide/2-acrylamido-2-methylpropanesulfonic Acid that is not theHydrated Crystalline Form (75/25 Mole %)

The copolymer is prepared as in Example 19, replacing the2-acrylamido-2-methylpropanesulfonic acid of hydrated crystalline form(Example 2) with 2-acrylamido-2-methylpropanesulfonic acid synthesizedin example 1 that is not the hydrated crystalline form.

The invention claimed is:
 1. A (co)polymer of2-acrylamido-2-methylpropanesulfonic acid, in its acidic and/or salifiedform, wherein at least a portion of the2-acrylamido-2-methylpropanesulfonic acid is in hydrated crystallineform and has a powder X-ray diffraction pattern including peaks at10.58°, 11.2°, 12.65°, 13.66°, 16.28°, 18.45°, 20°, 20.4°, 22.5°, 25.5°,25.88°, 26.47°, 28.52°, 30.28°, 30.8°, 34.09°, 38.19°, 40.69°, 41.82°,43.74°, and 46.04° degrees 2-theta, all peak values being +/−0.1°. 2.The (co)polymer according to claim 1, wherein the (co)polymer comprisesone or more additional monomers selected from the group consisting ofnon-ionic monomers, cationic monomers, zwitterionic monomers, anionicmonomers distinct from 2-acrylamido-2-methylpropanesulfonic acid beingin hydrated crystalline form and having a powder X-ray diffractionpattern including peaks at 10.58°, 11.2°, 12.65°, 13.66°, 16.28°,18.45°, 20°, 20.4°, 22.5°, 25.5°, 25.88°, 26.47°, 28.52°, 30.28°, 30.8°,34.09°, 38.19°, 40.69°, 41.82°, 43.74°, and 46.04° degrees 2-theta, allpeak values being +/−0.1°, and mixtures thereof.
 3. The (co)polymeraccording to claim 1, wherein the (co)polymer is a copolymer of thehydrated crystalline form of 2-acrylamido-2-methylpropanesulfonic acidand at least one non-ionic monomer.
 4. The (co)polymer according toclaim 1, wherein the (co)polymer is a copolymer of the hydratedcrystalline form of 2-acrylamido-2-methylpropanesulfonic acid and atleast one non-ionic monomer selected from the group consisting ofacrylamide; N-isopropylacrylamide; N,N-dimethylacrylamide;N-vinylformamide; acryloyl morpholine; N,N-diethyl acrylamide;N-tert-butyl acrylamide; N-tert-octylacrylamide; N-vinylpyrrolidone;N-vinylcaprolactam; N-vinyl-imidazole, hydroxyethyl methacrylamide,hydroxypropylacrylate, isoprenoln diacetone acrylamide, and mixturethereof.
 5. The (co)polymer according to claim 2, wherein the anionicmonomer is selected from the group consisting of acrylic acid,methacrylic acid, itaconic acid, crotonic acid, maleic acid, fumaricacid, acrylamide undecanoic acid, acrylamide 3-methylbutanoic acid,maleic anhydride; vinylsulfonic acid, vinylphosphonic acid,allylsulfonic acid, methallylsulfonic acid,2-methylidenepropane-1,3-disulfonic acid, 2-sulfoethylmethacrylate,sulfopropylmethacrylate, sulfopropylacrylate, allylphosphonic acid,styrene sulfonic acid, 2-acrylamido-2-methypropane disulfonic acid,salts of these monomers, and mixture thereof.
 6. The (co)polymeraccording to claim 2, wherein the cationic monomer is selected from thegroup consisting of quaternized dimethylaminoethyl acrylate, quaternizeddimethylaminoethyl methacrylate, dimethyldiallylammonium chloride,acrylamido propyltrimethyl ammonium chloride, methacrylamidopropyltrimethyl ammonium chloride, and mixture thereof.
 7. The(co)polymer according to claim 2, wherein the zwitterionic monomer isselected from the group consisting of 2-((2-(acryloyloxy)ethyl)dimethylammonio) ethane-1-sulfonate, 3-((2-(acryloyloxy)ethyl)dimethylammonio) propane-1-sulfonate, 4-((2-(acryloyloxy)ethyl)dimethylammonio) butane-1-sulfonate, [2-(acryloyloxy)ethyl)](dimethylammonio) acetate, 2-((2-(methacryloyloxy) ethyl)dimethylammonio) ethane-1-sulfonate, 3-((2-(methacryloyloxy) ethyl)dimethylammonio) propane-1-sulfonate, 4-((2-(methacryloyloxy) ethyl)dimethylammonio) butane-1-sulfonate, [2-(methacryloyloxy)ethyl](dimethylammonio) acetate, 2-((3-acrylamidopropyl) dimethylammonio)ethane-1-sulfonate, 3-((3-acrylamidopropyl) dimethylammonio)propane-1-sulfonate, 4-((3-acrylamidopropyl) dimethylammonio)butane-1-sulfonate, [3-(acryloyloxy) propyl] (dimethylammonio) acetate,2-((3-methacrylamidopropyl) dimethylammonio) ethane-1-sulfonate,3-((3-methacrylamidopropyl) dimethylammonio) propane-1-sulfonate,4-((3-methacrylamidopropyl) dimethylammonio) butane-1-sulfonate,[3-(methacryloyloxy)propyl)] (dimethylammonio) acetate, and mixturethereof.
 8. The (co)polymer according to claim 1, wherein the(co)polymer is linear, structured or crosslinked.
 9. The (co)polymeraccording to claim 1, wherein the (co)polymer comprises at least oneLCST group.
 10. The (co)polymer according to claim 1, wherein the(co)polymer comprises at least one UC ST group.
 11. The (co)polymeraccording to claim 1, wherein the (co)polymer has an average molecularweight by weight of between 1 and 40 millions g/mol.
 12. The (co)polymeraccording to claim 1, wherein the hydrated crystalline form of2-acrylamido-2-methylpropane sulfonic acid presents a Fourier transforminfrared spectrum comprising peaks at 3280 cm⁻¹, 3126 cm⁻¹, 1657 cm⁻¹,1595 cm⁻¹, 1453 cm⁻¹, 1395 cm⁻¹, 1307 cm⁻¹, 1205 cm⁻¹, 1164 cm⁻¹, 1113cm⁻¹, 1041 cm⁻¹, 968 cm⁻¹, 885 cm⁻¹, 815 cm⁻¹, and 794 cm⁻¹, all peakvalues being +/−8 cm⁻¹.
 13. The (co)polymer according to claim 1,wherein the hydrated crystalline form of 2-acrylamido-2-methylpropanesulfonic acid presents minimum ignition energy greater than 400 mJ. 14.The (co)polymer according to claim 1, wherein the hydrated crystallineform of 2-acrylamido-2-methylpropane sulfonic acid presents 4 thermalphenomena with the Differential Scanning calorimetry technique at 70°C., 100° C., 150° C. and 190° C., all +/−10° C.
 15. The (co)polymeraccording to claim 1, wherein the hydrated crystalline form of2-acrylamido-2-methylpropane sulfonic acid has awater/2-acrylamido-2-methylpropane sulfonic acid molar ratio of 1:1.